Many intracellular pathogens that infect man fail to induce detectable levels of antibodies until after disease symptoms appear. Thus, early diagnosis by classical antibody-based serological techniques is problematic. In such cases, an easy, sensitive, specific, and rapid method for identification of the pathogen itself is required. EntreMed has developed proprietary technology using flow cytometry to detect intracellular pathogens in specific and sensitive screening assays. Flow cytometry differentiates cell populations based on their size, internal complexity, and antibody-defined surface markers. Monoclonal antibodies can also be used in this system to identify pathogens inside cells. The short-term objective of this proposal is to refine and increase the sensitivity of a flow cytometric technique for diagnosis of active Leishmania-infections. The long-term objective, however, is to develop this method as a platform technology for diagnosis of infections caused by a range of intracellular pathogens. Most hospitals routinely use flow cytometric analyses for diagnosis of certain diseases (HIV, leukemia, etc.). Thus, a well defined, technologically informed commercial market presently exists for this assay. A large pharmaceutical company that participated in the concept's early development, remains interested in possible commercial application of the technology, if feasibility is demonstrable in Phase I.